AU2004240456B2 - Method and apparatus for representing image granularity by one or more parameters - Google Patents

Description

WO 2004/105250 PCT/US2004/009866 1 METHOD AND APPARATUS FOR REPRESENTING IMAGE GRANULARITY BY ONE OR MORE PARAMETERS 5 CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application Serial No 60/470,712, filed May 15, 2003, the teachings of which are incorporated herein. 10 TECHNICAL FIELD This invention relates to a technique for simulating film grain . 15 BACKGROUND OF THE INVENTION Motion picture films comprise silver-halide crystals dispersed in an emulsion, which is coated in thin layers on a film base. The exposure and development of these crystals form the photographic image consisting of discrete tiny particles of 20 silver. In color negatives, where the silver is chemically removed after development, tiny blobs of dye occur on the sites where the silver crystals form. These smalls specks of dye are commonly called 'grain' in color film. Grain appears randomly distributed on the resulting image because of the random formation of silver crystals on the original emulsion. Within a uniformly exposed area, some crystals develop 25 after exposure while others do not. Grain varies in size and shape. The faster the film, the larger the clumps of silver formed and blobs of dye generated, and the more they tend to group together in random patterns. The grain pattern is typically known as 'granularity'. The naked eye cannot distinguish individual grains, which vary from 0.0002 mm to about 0.002 30 mm. Instead, the eye resolves groups of grains, referred to as blobs. A viewer identifies these groups of blobs as film grain. As the image resolution becomes larger, the perception of the film grain becomes higher. Film grain becomes clearly WO 2004/105250 PCT/US2004/009866 2 noticeable on cinema and high-definition images, whereas film grain progressively loses importance in SDTV and becomes imperceptible in smaller formats. Motion picture film typically contains image-dependent noise resulting either from the physical process of exposure and development of the photographic film or 5 from the subsequent editing of the images. The photographic film possesses a characteristic quasi-random pattern, or texture, resulting from physical granularity of the photographic emulsion. Alternatively, a similar pattern can be simulated over computed-generated images in order to blend them with photographic film. In both cases, this image-dependent noise is referred to as grain. Quite often, moderate 10 grain texture presents a desirable feature in motion pictures. In some instances, the film grain provides visual cues that facilitate the correct perception of two-dimensional pictures. Film grade is often varied within a single film to provide various clues as to time reference, point of view, etc. Many other technical and artistic uses exist for controlling grain texture in the motion picture.industry. Therefore, preserving the 15 grainy appearance of images throughout image processing and delivery chain has become a requirement in the motion picture industry. Several commercially available products have the capability of simulating film grain, often for blending a computer-generated object into natural scene. Cineon@ from Eastman Kodak Co, Rochester New York, one of the first digital film applications 20 to implement grain simulation, produces very realistic results for many grain types. However, the Cineon@ application does not yield good performance for many high speed films because of the noticeable diagonal stripes the application produces for high grain size settings. Further, the Cineon@ application fails to simulate grain with adequate fidelity when images are subject to previous processing, for example, such 25 as when the images are copied or digitally processed. Another commercial product that simulates film grain is Grain SurgeryTM from Visual Infinity Inc., which is used as a plug-in of Adobe @ After Effects 0. The Grain SurgeryTM product appears to generate synthetic grain by filtering a set of random numbers. This approach suffers from disadvantage of a high computational 30 complexity.

3 None of these past schemes solves the problem of restoring film grain in compressed video restoration. Film grain constitutes a high frequency quasi random phenomenon that typically cannot undergo compression using conventional spatial and temporal methods that take advantage of 5 redundancies in the video sequences. Attempts to process film-originated images using MPEG-2 or ITU-T/ISO H.264 compression techniques usually result in either an unacceptably low degree of compression or complete loss of the grain texture. Thus, there exists a need for a technique for representing the film grain 10 characteristics through one or more of a set of parameters. A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was, in Australia, known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims. 15 SUMMARY OF THE INVENTION According to an aspect of the present invention, there is provided a method for simulating film grain comprising the steps of: 20 receiving image information representative of an image; receiving film grain information that includes at least one parameter specifying at least one film grain attribute; and simulating the film grain in accordance with the at least one parameter and based in part on at least one characteristic of the received image into which 25 film grain is to be added. According to another aspect of the present invention, there is provided a method for simulating film grain comprising the steps of: receiving image information representative of an image from which film grain has been at least attenuated; 30 receiving film grain information that includes at least one parameter among a set of possible parameters specifying different attributes of the film grain previously in the image; selecting a model for simulating grain; W:\SASKIA\Patent Spec\1RN758949. 23.06.09.doc 3a simulating the film grain in accordance with the selected model and the at least one parameter; and based on at least one characteristic of the received image into which film grain is to be added; and merging the simulated film grain into the image. 5 According to yet another aspect of the present invention, there is provided an apparatus for simulating film grain, comprising: means for receiving image information representing an image; means for receiving film grain information that includes at least one parameter specifying a film grain attribute; and 10 means for simulating the film grain in accordance with the at least one parameter and based on at least one characteristic of the received image into which film grain is to be added. According to still another aspect of the present invention, there is provided apparatus for simulating film grain, comprising: 15 first means for: (1) receiving image information representing an image from which film grain has been substantially attenuated; (2) receiving film grain information that includes at least one parameter among a set of possible parameters specifying different attributes of the film grain; (3) selecting a model for simulating grain; and (4) simulating the film grain in accordance with the 20 selected model and the at least one parameter; and based on at least one characteristic of the received image into which film grain is to be added; and second means for blending the simulated film grain with the image. Briefly, in accordance with a preferred embodiment of the present principles, there is provided a technique for simulating film grain. The technique 25 commences upon the receipt of image information representative of an image from which film grain has been at least attenuated. Accompanying the image information is film grain information that includes at least one parameter among a set of possible parameters specifying different attributes of the film grain previously in the image. A model is selected for simulating grain and the film 30 grain is simulated film grain in accordance with the selected model and the at least one parameter. The simulated film grain is then merged into the image. WASASKIA\Patent Spec\IRN758949. 23.06.09.doc 3b BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 illustrates a block diagram of a first embodiment of a system 5 in accordance with the present principles for simulating film grain in accordance with the present principles; FIGURE 2 illustrates a block diagram of a second embodiment of a system in accordance with the present principles for simulating film grain in accordance with the present principles; and W:\SASKIA\Patent Spec\IRN758949. 23.06.09.doc WO 2004/105250 PCT/US2004/009866 4 FIGURE 3 illustrates a block diagram of a third embodiment of a system in accordance with the present principles for simulating film grain in accordance with the present principles. 5 DETAILED DESCRIPTION FIGURE 1 depicts a block schematic diagram of a first embodiment of a system 10 in accordance with the present principles for performing film grain simulation in accordance with the present principles. The system 10 includes a Film 10 Grain Remover 22 that serves to remove the film grain from an input video stream 12 to yield a filtered video stream 24 received at a Video Encoder 13. Film grain removal constitutes a particular case of noise filtering where the noise signal appears correlated with the image signal. Thus, the Film Grain Remover 22 can take the form of a classical image filter, although such a filter will not necessarily provide optimal 15 performance. The Video Encoder 13 encodes the filtered video stream 24 to yield a coded video stream 14 for receipt at a Video Decoder 15 that decodes the coded stream to yield a decoded video stream 16. The Video Encoder 13 and the Video Decoder 15 utilize the same video coding scheme as are well known in the art. For example, the video coding scheme could comprise the ITU-T H.264 video-coding 20 standard, or another type of block-based coding. Encoders and decoders that utilize the MPEG-2 and the ITU-T H.264 standard are well known. The system 10 also includes a Film Grain Characterizer 23 that receives the input video stream 12 and the filtered video strearn 24. From these video streams, the Film Grain Characterizer 23 outputs a message, hereinafter referred to as a grain 25 message, that contains an identity of a model for simulating grain, as well at least one of a set of several parameters, including correlation parameters, intensity independent parameters and intensity-dependent parameters used by the identified model. As discussed in detail below, the parameters in the film grain message enable simulation of the original image-dependent noise using the identified model. 30 In the absence of any of the parameters, a default value is assigned to that missing parameter. (indeed, if no model is identified, a default model for film grain is assumed. In one embodiment, the Film grain characterizer 23 generates the WO 2004/105250 PCT/US2004/009866 5 parameters in accordance with a model based on the physical process of exposure and development of the photographic film or upon processes added during the subsequent editing of the images. Following generation of the grain message, a Film Grain characterization 5 information Encoder 26 encodes the message for transmission to a Film Grain characterization information Decoder 28 in-band or out-of band from, the encoded video stream 14 transmitted by the Video Encoder 13 to a the Video Decoder 15. Both the Video Encoder 13 and the Film Grain characterization information Encoder 26 use the same encoding scheme. Thus, for example, when the Encoder 26 utilizes 10 the ITU-T H.264 video-coding standard for encoding, the coded film grain characterization information stream 27 can take the form of the film grain Supplemental Enhancement Information (SEI) message as defined in the ITU-T H.264 video coding standard. The Film Grain characterization information Decoder 28 decodes the coded 15 film grain message 27 to yield a decoded film grain characterization information stream 29 for input to a Film Grain Restoration Processor 30. As described in detail hereinafter, the Processor 30 will simulate the film grain with a model identified in the grain message using parameters in message. In the absence of the identification of the model, the Processor 30 will assume a default mode. Likewise, in the absence of 20 a specified value of a given parameter, the Processor 30 will assume a default value for that parameter. In a preferred embodiment, the grain message 25 of FIG. 1 will typically include one or more correlation parameters specifying Spatial Correlation, Aspect Ratio, Color Correlation, and Temporal Correlation. Each of these parameters is 25 discussed below Spatial correlation In an exemplary embodiment, the image-dependent correlation of the film 30 grain in the spatial domain can be modeled with at least one parameter, Spatial Correlation. The measured spatial correlation determines the size of the blobs. A WO 2004/105250 PCT/US2004/009866 6 second order auto regression model and a convolution model for the Spatial Correlation are described hereinafter. Aspect Ratio 5 Ideally, film grain should appear isotropic, with identical characteristics both in X and Y direction. However, in practice, the film grain actually can appear stretched in one direction, often resulting from factors related to film recording, such as the use anamorphic optics or non-square detector geometry. For that reason, when modeling 10 film grain, an intensity-independent parameter representing the aspect ratio factor will complement the spatial correlation measure. The aspect ratio of the grain blobs is specified with at least one parameter. Color Correlation 15 In accordance with the present principles, the layer-dependency of the film grain in color images is represented using color correlation. The measured color correlation determines the perceived tint of the grain. A weak color correlation implies that grain blobs created in the different color layers randomly overlay each 20 other. Consequently, a viewer will perceive the grain as colored. A high color correlation implies that the grain blobs on one color component depend on other color components. In this case, a viewer will perceive the grain as monochromatic. Temporal correlation 25 The temporal correlation of the grain in sequences is represented by at least one parameter. Grain by itself cannot exhibit any temporal correlation between frames, but the introduction of a parameter representing temporal correlation can help to simulate other observed effects caused by the editing of the film. 30 WO 2004/105250 PCT/US2004/009866 7 Noise intensity In conjunction with the previously discussed parameters representing the dependency of the film grain with the film image, a need exists to represent the 5 intensity of the noise arising from the random processes that originate the film grain. Noise intensity can vary for each color component and will depend on the film image. The intensity of the grain determines the level in which noise is perceived in the image. Small grain intensity levels introduce small variations in the original image and hardly appear noticeable. High intensity levels become clearly visible as peaks 10 superimposed in the image. Other Parameters In addition to the parameters discussed above, the grain message can also 15 include parameters that identify the color space in which to add the film grain, and the blending mode used to blend the grain with the video signal. Note that a different set of parameters could be transmitted for each color component and for different intensity levels of the film image. It is well known for example that film grain depends on the local intensity of the image, and that different color components can have 20 different grain depending on the type of film stock. The film grain characterizer 23 of FIG. 1 can generate different sets of parameters in accordance with the intensity levels of the image. If desired, the Film grain decoder 28 can interpolate the set of parameters to various intensity levels in order to derive a smooth transition of the film grain characteristics. 25 In order to interpret the set of parameters, the Film grain decoder 28 must have a specification of the model that generates the parameters. To understand how such a model can be specified, the following mathematical relationships will prove useful. First, the decoded image pixel value at image position (x, y), color channel c, and frame number t is represented by l(x, y, c, t). For convenience, assume that 30 pixel values are scaled to have maximum value of one. Further, assume an RGB image representation (c = 1, 2, or 3), although this model can be directly to monochromatic images and, with obvious modifications, to YUV representation.

WO 2004/105250 PCT/US2004/009866 8 With an additive grain model, grain simulation changes each pixel value to J(x, y, c, t) where J(x, y, c, t) is given by the relationship: (1) J(x, y, c, t) = l(x, y, c, t) + G(x, y, c, t, L(x, y, t)), 5 where L(x, y, t) is a measure of local intensity in the image and G(x, y, c, t, L(x, y, t)) defines the grain value. One possible implementation is to define L as luminance, or a weighted sum of intensities l(x, y, c, t) over all color channels. The additive model given by equation (1) is appropriate when a logarithmic 10 intensity scale is used. For linear scale, the model of equation (1) can be replaced by the following multiplicative mode: (1a) J(x, y, c, t) = l(x, y, c, t) * (1 + G(x, y, c, t, L(x, y, t))). 15 Whether an additive or a multiplicative grain model is implemented will depend on the format of the decoded image. In general, grain should comprise small fraction of maximum pixel value. The following describes some examples of different kind of models for extracting a set of parameters in accordance with the present invention. 20 1. Autoregressive simulation of film grain pattern In an exemplary embodiment, a second order auto regression scheme can be used to model spatial correlation and a first order regression scheme can be used to model cross-color and temporal correlations. All correlation factors depend on 25 intensity of the decoded image. Horizontal and vertical spatial correlation factors are related by a constant aspect ratio factor. Under such conditions, the following formula will yield simulated grain values, (2) G(x, y, c, t, L) = p(c, L)*N + 30 q(c, L) (G(x-1, y, c, t, L) + A * G(x, y-1, c, t, L) + r(c, L) * A * (G(x-1, y-1, c, t, L) + G(x+1, y-1, c, t, L)) + WO 2004/105250 PCT/US2004/009866 9 s(c, L) * (G(x-2, y, c, t, L) + A * A * G(x, y-2, C, t, L)) +u(c, L) * G(x, y, c-1, t, L) v(c, L) * G(x, y, c, t-1, L) 5 where N is a random value with normalized Gaussian distribution, A is a constant pixel aspect ratio, p, q, r, s, u, and v are correlation parameters. Parameter u is always zero for the first color channel, and the grain value G assumed to be zero whenever any index is out of range. As can be seen from the structure of equation (2), grain values for a given 10 pixel in a given color channel are calculated recursively using previously calculated grain values. Specifically, frames are calculated in order of increasing frame number (i.e., increasing t). Within each frame, color channels processing occurs in order of increasing color channel number (i.e., increasing c). Within each color channel, pixels are rasterized horizontally and then vertically in order of increasing x and y. 15 When this order is followed, all grain values required by equation (2) are automatically calculated in advance. Under certain circumstances, vertical rasterization proves more practical, i.e. pixels processing occurs by columns first. In such cases, equation (2) will require a slight modification to use only previously calculated values: 20 (2a) G(x, y, c, t, L) = p(c, L)*N + q(c, L) *(G(x-1, y, c, t, L) + A * G(x, y-1, c, t, L)) + r(c, L) A * (G(x-1, y-1, c, t, L) + G(x-1, y+1, c, t, L)) + s(c, L) * (G(x-2, y, c, t, L) + A * A * G(x, y-2, c, t, L)) + 25 u(c, L) *G(x, y, c-1, t, L) + v(c, L) * G(x, y, c, t-1, L). Implementing equation (2) or equation (2a)) requires certain minimum decoder capabilities. First, the Film Grain Information decoder 28 must perform all 30 calculations real time. Second, the Film Grain Information decoder 28 needs to keep a number of previously calculated grain values in memory. Specifically, to implement temporal correlation (i.e., last term in equations (2) and (2a)), the Film Grain WO 2004/105250 PCT/US2004/009866 10 Information decoder 28 needs to keep grain values for a full previous frame. From this perspective, it is important that the model of equation (2) allow gradual scaling down requirements with some degradation of fidelity. A system with slightly lower fidelity could ignore the last (temporal) term in 5 equation (2). Doing so would eliminate the need to have an additional frame buffer to keep grain values from previous frame. Further cost savings would result by neglecting those terms in equation (2) that depend on s(c, L). Doing so eliminates need to store a second previous row in memory and reduces number of calculations. Neglecting diagonal correlations described by terms with r(c, L), and so on will 10 achieve a further reduction of complexity. The lowest quality grain simulator will use only white noise term. Whenever a term is neglected in a scaled-down system, a benefit occurs if the Film Grain Information decoder 28 adjusts the remaining parameters so that the effective first-order correlation and even more importantly, the autocorrelation (noise 15 power) remain the same as they would in a full-scale implementation of the model embodied by equation (2). The same adjustment should occur for the first rows and columns of each frame in the absence of the availability of all of the previous grain values. The flexibility of the model embodied in equation (2) will become further 20 apparent by setting parameters p, q, r, and s to zero for all but first color channel, and by setting the color correlations u(c, L) for c > 1 to 1. Under such conditions, the grain becomes completely monochromatic. This set of parameters values can describe the case for color variations washed out by previous YUV 4:2:0 transformation of the color space. 25 For a set of three colors, the model of equation (2) describes the grain pattern in terms of a group of seventeen parameters for each luminance level, plus an aspect ratio that does not depend on luminance. Luminance-dependent parameters can be encoded for several fixed luminance levels. The decoder will interpolate parameters values for intermediate luminance levels. 30 Grain parameters do not have to be represented exactly in the form of equation (2). For example, any one-to-one transform of the parameters could be WO 2004/105250 PCT/US2004/009866 11 used. In addition, different set of reference intensity levels could be used for different parameters and different interpolation schemes could be used, etc. 2. Convolution in the spatial domain to simulate the film grain 5 pattern In another exemplary embodiment, the film grain pattern can be simulated by convolving a set of random numbers x by a linear, time-invariant, digital-filter h defined in the form: 10 (3) h = (ho, h 1 , h 2 , h 3 , ... hn) This states that the filter output simulating film grain y(n) is the convolution of the input x(n) with the filter impulse response h(n): 15 n (4) y(n)= Ix(i)h(n - i) = (x * h)(n) i=o Although equation (4) yields a simulation in one dimension, a two-dimensional pattern could be obtained by concatenating the vertical and horizontal convolutions in 20 one dimension. Under such circumstances, the coefficients of the filter should be transmitted in addition to the aspect ratio factor. A Film Grain Information decoder 28 with limited capabilities can limit the spatial size of the convolution kernel, which will result in decreased memory and processing power requirements. 25 3. Filtering in a transformed domain to simulate the film grain pattern As discussed previously, convolving the impulse response of a filter h with a set of random numbers x can characterize the film grain pattern. This same 30 operation can also be described by multiplication in the frequency domain by the WO 2004/105250 PCT/US2004/009866 12 Fourier Transform of the impulse response H and the Fourier Transform of the set of random numbers X: (5) Y(u) = X (u) -H(u) 5 Filtering in the frequency domain affords an advantage because it is computationally faster if a Fourier transform of the image is available for example as part of filtering or compression process." The following set of parameters yielded satisfactory results to represent 10 image-dependent grain according in accordance with the present principles. These parameters assume an autoregressive method of simulating grain. Parameters for other methods would be represented by similar tables. Color space: logarithmic RGB 15 Blending mode: additive Aspect ratio: 1 Number of intensity levels: 3 Parameters for the R component: q r u v p 20 level [ 0, 84]: 0.1 .01 0.0 0.2 0.02 level [85,168]: 0.1 .01 0.0 0.15 0.03 level [169,255]: 0.3 -.01 0.0 0.15 0.05 Parameters for the G component: q r u v p 25 level [ 0, 84]: 0.3 0.0 0.1 0.2 0.01 level [85,168] : 0.2 .01 0.1 0.15 0.03 level [169,255]: 0.1 -. 01 0.2 0.1 0.05 Parameters for the B component: 30 q r u v p level [ 0, 84]: 0.4 .01 0.1 0.2 0.02 level [85,168]: 0.1 0.0 0.1 0.15 0.03 WO 2004/105250 PCT/US2004/009866 13 level [169,255]: 0.1 0.0 0.2 0.1 0.04 Correlation parameters not shown in this table are set to 0. After specifying the color space, the blending mode, the aspect ratio and the number 5 of intensity levels for which different parameters are defined, the film grain on each color component is encoded. Note that only the data in italics in addition to some level (intensity) information has to be transmitted. FIGURE 2 depicts a second embodiment 10' of a system for simulating film grain in accordance with the present principles. The system 10' shares many of the 10 same elements as the system 10 of FIG. 1 and like reference numbers describe like elements. Indeed, the system 10' of FIG. 2 differs only in the absence of the Film Grain characterization information Encoder 26 and Film Grain characterization information Decoder 28 of FIG. 1. The system 10' of FIG. 2 uses the Video Encoder 13 and Video Decoder 15 to encode and decode respectively the film grain 15 characterization information 25 output of the Film Grain Characterizer 23. The system 10' of FIG. 2 requires the use of a video coding standard that supports the transmission film grain characterization information as parallel enhancement information. FIGURE 3 depicts a third embodiment 10" of a system for simulating film grain 20 in accordance with the present principles. The system 10" shares many of the same elements as the system 10' of FIG. 2 and like reference numbers describe like elements. Indeed, the system 10" of FIG. 3 differs only in the absence of the Film Grain Remover 22 of FIG. 2. The system 10" of FIG. 3 uses the reconstructed images available at the Video Encoder 13 to simulate the result of removing film 25 grain. The system 10" of FIG. 3 affords two advantages as compared to the systems 10 of FIG. 1 and 10' of FIG 2. First, the system 10" of FIG. 3 reduces the computational complexity related to film grain removal, and secondly, it adapts the film grain characterization to the amount of film grain suppressed by the Video Encoder 13. Once the Film Grain Characterizer of FIG. 3 disposes of both the input 30 video 12 with film grain, and a reconstructed video 24 resulting from Video Encoder 13, it can accomplish the task of characterizing the observed film grain.

14 The foregoing describes a technique for simulating film grain in a video signal. While the film grain simulation technique has been described in connection with the encoding and decoding of a video signal, the technique has equal applicability for other purposes, such as for example post-production of 5 motion picture films for example. In this regard, the original image could exist as image information in a form other than a compressed video signal, and the film grain information could exist in a form other than as a message, such as an SEI message. For example, the image information could exist in one of a variety of different formats that exist in the art. 10 Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps of components, or group thereof. 15 W:\SASKIA\Patent Spec\lRN758949. 23.06.09.doc

Claims (23)

1. A method for simulating film grain comprising the steps of: receiving image information representative of an image; 5 receiving film grain information that includes at least one parameter specifying at least one film grain attribute; and simulating the film grain in accordance with the at least one parameter and based in part on at least one characteristic of the received image into which film grain is to be added. 10

2. The method according to claim 1 further including the step of blending the simulated film grain into the image.

3. The method according to claim 1 or 2 wherein the step of receiving film 15 grain information includes the step of receiving a plurality of parameters each indicative of a film grain attribute.

4. The method according to claim 3 wherein the set of parameters includes a plurality of correlation parameters and a plurality of intensity-independent 20 parameters.

5. The method according to claim 4 wherein at least one correlation parameter defines a spatial correlation in a perceived pattern of film grain. 25

6. The method according to claim 4 wherein at least one correlation parameter defines a correlation between color layers.

7. The method according to claim 4 wherein at least one correlation parameter defines a temporal correlation resulting from previous processing the 30 image sequence.

8. The method according to claim 4 wherein at least one intensity independent parameter defines an aspect ratio of the film grain. WASASKIA\Patent Spec\IRN758949. 23.06.09.doc 16

9. The method according to any one of claims 1 to 8 wherein at least one parameter defines intensity of a random component of the film grain.

10. The method according to claim 4 wherein at least one of the intensity 5 independent parameters defines a color space and blending mode operation used to merge the simulated film grain with the image.

11. The method in accordance with claim 4 where the set of parameters are obtained in accordance with a second order auto regression representation of the 10 spatial correlation and a first order regression representation of the cross-color and temporal correlations.

12. The method according to any one of claims 1 to 4 wherein the at least one parameter describes a spatial pattern of the grain. 15

13. The method according to claim 12 wherein the at least one parameter is established in accordance with a spatial convolution mode.

14. The method according to claim 12 wherein the at least one parameter is ?0 obtained from cut frequencies of a filter in the Fourier domain.

15. A method for simulating film grain comprising the steps of: receiving image information representative of an image from which film grain has been at least attenuated; 25 receiving film grain information that includes at least one parameter among a set of possible parameters specifying different attributes of the film grain previously in the image; selecting a model for simulating grain; simulating the film grain in accordance with the selected model and the at least 30 one parameter and based on at least one characteristic of the received image into which film grain is to be added; and merging the simulated film grain into the image. C:\poftword\SPEC-758949.doc (17105/10) 17

16. The method according to claim 15 wherein the step of selecting the model further comprises the step of selecting an additive grain model.

17. The method according to claim 15 wherein the step of selecting the model 5 further comprises the step of selecting a multiplicative grain model.

18. The method according to claim 15 wherein the step of selecting the model further comprises the step of selecting a model that simulates the film grain by convolving a set of random numbers by a linear, time-invariant, digital-filter h defined 10 in the form of: h =(h., h1, h2, h3,... h,) wherein the set of parameters includes filter coefficients.

19. The method according to claim 15 wherein the step of selecting the model 15 further comprises the step of multiplying in the frequency domain by a Fourier Transform of an impulse response H and a Fourier Transform set of random numbers to yield a simulated grain result Y(u) in accordance with the relationship: Y (u) = X (u) - H (u) ?0

20. Apparatus for simulating film grain, comprising: means for receiving image information representing an image; means for receiving film grain information that includes at least one parameter specifying a film grain attribute; and means for simulating the film grain in accordance with the at least one 25 parameter and based on at least one characteristic of the received image into which film grain is to be added.

21. The apparatus according to claim 20 further including means for blending the simulated film grain with the image. 30

22. Apparatus for simulating film grain, comprising: first means for: (1) receiving image information representing an image from which film grain has been substantially attenuated; (2) receiving film grain information that includes at least one parameter among a set of possible parameters specifying C:\pof~word\SPEC-758949.doc (17/05/10) 18 different attributes of the film grain; (3) selecting a model for simulating grain; and (4) simulating the film grain in accordance with the selected model and the at least one parameter; and based on at least one characteristic of the received image into which film grain is to be added; and 5 second means for blending the simulated film grain with the image.

23. The apparatus according to claim 22 wherein the model selected by the first means comprises an additive grain model. C:\pof\word\SPEC-758949.doc (17/05/10)